The present invention relates to colored glass.
It should be understood that throughout this specification the symbol % means percentage by weight.
Colored glass containing colored ions exhibits its expected functions by absorbing light, either broadly or sharply, in the ultraviolet, visible or near-infrared region of the spectrum. Examples of colored glass contain at least one of such ions as Fe, Ni, Co, V, Ce, etc. as incorporated in the base glass. These types of colored glass have been used in distinct applications according to their transmission and absorption characteristics, for example as optical filters such as neutral density filters, blue filters, etc., sunglasses, colored glasses for containers, colored plate glass and so on.
However, the conventional colored glass has not fully satisfied the performance requirements in such respective applications. For example, when colored glass is used for sunglasses, it is not only required to have the expected transmission characteristic with regard to visible light but desirably should intercept light in the ultraviolet region, which is harmful to the eye, with substantial thoroughness. Actually, however, when the absorption of visible light is set to the transmittance value suited to sunglasses, the conventional colored glass passes most of the harmful light in the ultraviolet spectrum, too. On the other hand, if an UV absorbing colored ion, such as Ce, is incorporated in glass to the extent completely absorbing light in the ultraviolet region, light in the visible region is also mostly absorbed because of its broad absorption characteristic, with the result that the colored glass cannot discharge the function required of sunglasses. Therefore, whenever the conventional colored glass is used for sunglasses, either the transmittance characteristics of visible light or that of ultraviolet light has to be sacrificed.